Precise control of some motor designs is possible using pulse count technology. According to this position feedback technique, a system monitors brush commutation pulses or current spikes generated during the rotation of the motor. These detected pulses are then appropriately processed and counted, with the results sent to a controller that can then accurately determine and adjust the position of the motor shaft.
Unlike other motor control methods where the drive circuitry is often integrated with each motor, pulse count control is typically implemented through a centralized processor where it can be used to control multiple motors. Due to the large amount of processing, associated drive circuitry, and software required to implement the pulse count control of a motor, this integration through a centralized processor is typically chosen over integrating the drive circuitry into each individual motor as the latter becomes highly inefficient and not cost effective. This arrangement where the pulse count processing and motor drive circuitry are incorporated into a central processor or controller is illustrated in FIG. 1. Once the pulse count system is incorporated, the central controller 10 is wired directly to the motors 20A-20E that are to be controlled. One example of this typical arrangement can be found in automotive applications, where pulse count control is often desired for motors that are part of the heating, ventilation and air conditioning (HVAC) system of a vehicle. The typical HVAC system relies upon a centralized control head to oversee the operation and control of the system. This typical centralized control head contains the circuitry and programming required to coordinate the operation of the various subsystems of the HVAC system, along with control inputs that allow a vehicle occupant to activate and adjust the various systems, i.e. turn on the heater and increase the temperature of the vehicle interior. With the addition of pulse count control to the HVAC system, the centralized control head must be expanded to further include the pulse count control processor and motor drive circuitry needed to operate the various motors of the system.
However, difficulties arise due to the incorporation of the pulse count processing and motor drive circuitry into a centralized control head. Returning to the automotive example, the placement of the pulse count processing functions and motor drive circuitry within a central control head leads to the requirement that a relatively expensive microprocessor be used in the control head. Specifically, the control head has its own programming and processing requirements to execute. With the addition of the programming and processing requirements called for by the pulse count control system, the processing demands on the control head increase to the point that it requires a relatively powerful, and thus expensive, microprocessor in order for it to carry out its duties.
Beyond hardware costs, the incorporating of the pulse count processing and motor drive circuitry into a centralized control head leads to increased production costs due to the extreme variability between control heads of different vehicles. All vehicles can benefit from the use of pulse count technology to control the motors associated with its various systems. However, almost every type of vehicle has its own unique control head that has been designed or modified to meet the specific requirements of that vehicle type. Thus the control head for an automobile manufactured by Chrysler can be very different from the control head for an automobile manufactured by Ford. Similarly, the control heads for different vehicle models by the same manufacturer can be significantly different. As a result, there is no simple and standardized way to incorporate the circuitry and programming of a pulse count control system into a control head. For every different control head, or any time a design change is made to a control head, the pulse count control system has to be re-engineered to accommodate the existing differences or new changes. This results in significant time and expense associated with the process of incorporating a pulse count control system into a vehicle.
This excessive time and effort required to incorporate a pulse count control system into a vehicle also often prevents certain classes of customers from being able to obtain pulse count technology. For example, due to the wide variances in control heads, a manufacturer of pulse count motor control systems normally has to allocate significant time and resources into engineering a control system for each specific customer. As a result, it is not economically viable for the manufacturer to allocate the resources for small volume programs or customers. Thus the manufacturer is restricted in its ability to satisfy the demands of certain customers.
Therefore, the inventor hereof has recognized the need for a new device and method for implementing a pulse count motor control system that avoids the above restrictions.